Television



Jan. 18, 1944. D R DQNCASTER 2,339,256

TELEVISION Filed 001;. 3, 1941 Sheets-Sheet 2 I I I I INVENTOR 0am Pezer flancaazer ATTORNEYS Jan. 18, 1944. D. P. DONCASTER TELEVISION Filed Oct. 5, 1941 5 Sheets-Sheet 3 IVNVENTO flan Pea??? Dana-a: r

ATTORNEYS Patented Jan. 18, 1944 UNITED STATES PATENT OFFICE TELEVISION Dan Peter Doncaster, Long Island City, N. Y., as-

signor to Columbia Broadcasting System, Inc., New York, N. Y., a corporation of New York Application October 3, 1941, Serial No. 413,390

7 Claims. (Cl- 178-5.!)

This invention relates to color television, especially to color television apparatus of the type employing a rotating color filter element. The invention particularly contemplates the provision of .a form of rotating element and arrangement thereof with respect to a cooperating scanning device which will yield a compact assembly adapted to be conveniently housed in a cabinet.

In color television systems in which the object field is scanned successively in a plurality of colors and the signals transmitted to a receiver for reproduction, the use of rotating disks have heretofore been suggested. With properly shaped filter segments, such disks have been found to be entirely satisfactory from the standpoint of operation. However, the diameter of the disk must in general be somewhat more than twice the width of the screen area. Hence this requirement is a limiting factor in the design of a cabinet. For example, in a receiver employing a cathode ray tube, the tube must be located to one side of the axis of the disk. If the cabinet is kept to minimum dimensions, this req ires the viewing area to be at one side of the cabinet. Also, the diameter of the disk determines the minimum width of the cabinet. Withthe present tendency toward the use of large receiving tubes, so as to present large pictures, a somewhat bulky cabinet often results.

The present invention is especially directed to the provision of apparatus which will permit more freedom in the design of a compact, attractive cabinet.

In accordance with the invention, the rotating filter element is in the form of a cone, with the color filtersegments arranged around the conical surface of the cone. This shape permits the scanning device-to be positioned at least partially within the color filter element with the concave side of the conical surface toward the scanning device. The conically shaped filter element may be employed at the transmitter as well as at the receiver, but it is particularly important in the case of a receiver since the receiving scanning device is usually of large dimensions. In the case of a cathode ray receiving tube having a fluorescent screen on the end of the bulbous portion thereof, the greater part of the bulbous portion may be placed within the filter cone with the conical surface passing closely adjacent the fluorescent screen.

It is ordinarily not necessary to extend the filter segments completely to the apex of the cone, and the portion of the cone near the apex may be eliminated to save space, thereby forming a frusto-conical filter element. Furthermore, instead of using a cone having a circular base, or frustum thereof, a hexagonal or other shaped base may be employed. It will be understood that the term cone or conical surface as used herein includes these variations.

The invention will be more fully understood by reference to the specific embodiments illustrated in the drawings and the following description thereof. In the drawings: I

Figs. 1 and 2 are plan and front views, respectively, of one form of conical filter element and cooperating cathode ray receiver tube;

Fig. 3 is an end view of the filter element of Figs. 1 and 2;

Figs. 4 and 5 are plan and front views, respectively, of a conical filter element and associated scanning. device, the filter element havingfilter segments of different design;

Fig. 6 is an end view of the conical filter element of Figs. 4 and 5;

Figs. 7 and 8 are plan and front views, respectively, of a filter element having its axis diiferently positioned with -espect to the cathode ray receiver tube; and

Fig. 9 is an end view of the filter element of Figs. 7 and 8. v 7

Referring to Fig. l, the cathode ray receiver tube I is shown comprising an envelope having a bulbous portion 2 and an elongated neck 3 extending therefrom. The fluorescent screen is adjacent the face 4 of the bulbous portion 2, preferably being coated on the inner surface of the envelope. A rectangle 5 represents the two-dimensional picture area on which images are successively reproduced by a cathode ray beam from the electron gun 6. The cathode ray beam is deflected so as to scan area 5 in a plurality of laterally extending side-by-side lines at field scanning frequency by horizontal deflecting plates I energized by a suitable saw-tooth-wave generator 8 of line scanning frequency, and by vertical deflecting plates 9 energized by a. suitable sawtooth-wave generator ID of field scanning frequency. Magnetically deflecting coils may of course be employed instead of electrostatically deflecting plates.

The rotating filter element comprises a frame I5 having a conical shape and provided with a plurality of transparent color filters l6 arranged around the conical surface thereof. The filter element here shown is provided with six filter segments colored red, green and blue in succession. The numbers of colors, the particular colors selected, and the number of segments employed may be varied in accordance with considerations which will be understood by those skilled in the art.

The filter element is constructed to rotate about axis II by a suitable motor ll. As shown in Fig. 2, the axis is positioned laterally of the scanning area and in a horizontal plane. The cathode ray tube l is positioned partially within the conical surface with its image reproducing area closely adjacent the inner concave surface of the color filter element so that as the element rotates the area is exhibited successively through red, green and blue filters. As shown in the plan view of Fig. 1, the front edge It of the conical filter element is advantageously perpendicular to the axis of the-receiving tube I and hence extends generally parallel to the image reproducing surface of the tube in a lateral direction.

As the filter element rotates the color filters successively traverse the image reproducing area I. with the boundaries between filter segments traversing the area in substantially the low-frequency direction. In color television systems in which successive field images are to be reproduced in successive colors, the size of the conical filter element and the number of segments are selected with respect to the speed at which it rotates so that successive images are presented through successive filter segments, the filter segments traversing the image area at field-scanning frequency. At the present time each image field is reproduced in a series of horizontal sideby-side lines beginning at the top of the scanning area 5 and progressing to the bottom in a field-scanning period. Thus the conical filter element is arranged to rotate in the direction shown so that the boundaries traverse the area from top to bottom. Interlaced or non-interlaced scanning may be employed as desired. The

present invention is in no way limited to any particular scanning system. Any desired means may be provided for synchronizing the rotation of the conical filter element with the successive images.

In the conical filter element of Figs. l-3 the boundaries between filter segments extend toward the vertex of the cone, and only narrow boundaries are employed. The embodiment illustrated in Figs. 4-6 illustrate a manner in which the filter segments may be designed so as to economize filter material. In a cathode ray receiver tube having a fluorescent screen of relatively fast decay, it is necessary that a given line he exhibited through a given filter only at the time the line is being scanned and for a relatively short period thereafter. When the filter segments traverse the scanning area in the same direction that the lines are reproduced, only a relatively small filter segment is required in order to cover each line as it is scanned.

The proper form of such filter segments may be determined in a manner analogous to that described in detail in application Serial No. 355,839 of Peter C. Goldmark, filed September 7 1940, for "Color television." When successive images are reproduced in successive colors, the angle through which the conical filter element turns during a single field-scanning period is determined by the number of filter segments. For example, with the six segments shown, the cone turns through 80 during a field scanning interval. To design a single filter element an arbitrary starting position or the cone is selected and a line drawn on the surface of the cone overlying the top line of the scanning area. Then the cone is turned through a selected small angle, say 10, and a line drawn on the surface of the cone overlying the line of the image area which is scanned for that position of the cone. Since 10 represents one-sixth of the movement of the cone in a field scansion, the corresponding line of the image reproducing area will lie one-sixth of the distance from top to bottom of the image receiving area plus a small allowance to take into account the blanking interval. This procedure is repeated for successive angular positions of the cone and an area described so as to include all of the lines required to exhibit the image through the filter element. It is desirable of course to somewhat enlarge the filter segment so as to allow for some error in phasing the cone and also to permit the image receiving area to be viewed from positions somewhat above and below and to each side of the image receiving area. The filter segment thus designed may then be repeated at equal spacings around the conical surface.

The exact shape of th filter segments when so designed will vary with the relative dimensions of the cone and scanning area, the orientation of the axis and the position of the vertex (determined by extending the sides of the cone in th case of frusto-conical sections) with respect to the scanning area. However, with minimum dimensions the segments will generally be shaped so that the ends thereof towards the vertex are wider than the ends toward the base, as illustrated in Figs. 4-9.

For fluorescent screens having considerable afterglow, another series of lines can be drawn on the surface of the cone for angular positions of the cone angularly displaced from the previously selected positions by amounts representing the desired period for which a given line should remain exhibited through a color filter segment. This will result in a filter segment which extends somewhat farther around the periphery of the cone.

It will be observed that in both the embodiments of Figs. l-3 and 4-6 the width of the combined scanning tube and color filter element is considerably less than twice the diameter of the scanning tube, hence the width is much less than that required when a scanning disk is employed.

The embodiment of Figs. 7-9 has a similar advantage, and shows another position of the axis of the cone so as to illustrate the versatility of the invention. It will be understood that in the design of a color television receiver the positioning of the chassis, power supplies, motor, etc. require careful consideration so that the possibility of positioning the axis of the cone at various angles with respect to the tube ofiers desirable flexibility in overall design.

As shown in Fig. 8, the axis of the cone is oriented so that the vertex is below and to one side of the scanning area, instead of the axisbeing horizontal as in Figs. 2 and 5. However, it is still advantageous to have the front edge ll of the cone (Fig. 7) generally parallel to the scanning area. With the axis in this position, the shape and positioning of the filter segments on the conical surface, for minimum amounts of filter material, is somewhat different from that of Figs. 4-6. However, the method of design is the same. The cone is rotated through successive small angles and the lines on the cone overlying the corresponding scanning lines of the image reproducing area are determined so that the filter segments may be shaped and positioned to include the necessary lines as they are scanned.

In general it is preferred to have the vertex angle of the cone fairly acute, so that the actual dimensions of the cone may be kept to a minimum, However, considerable latitude in the angle selected and the positioning of the axis with respect to the canning device is allowed.

Although the drawings specifically show a cathode ray receiver tube employed in conjunction with the conical filter element, it will be understood that the conical filter element could be employed in connection with transmitter tubes also, if desired. A further-use is in connection with the type of large screen projector in which a. concave mirror is placed in front of a projector cathode ray tube. When used for color television, a filter element would be arranged to pass between the tube and the concave mirror. A color filter disk would intercept light rays from a considerable area of the mirror and hence would be undeirable. The shape of the filter element of the present invention is more adaptable to the limitations of this type of projector.

It will be understood that the present invention is not limited to the mere details of construction and arrangement of the elements disclosed, since many modifications may be made by those skilled in the art without departing from the spirit and scope of the invention.

I claim:

1. In color television apparatus, in combination, an electronic canning device comprising an envelope and an image area within said envelope and closely adjacent thereto, means for scanning said area in two dimensions in a plurality of side-by-side lines, and a rotatablesubstantially conical color filter element having a plurality of transparent color filter segments arranged therearound, the envelope of said scanning device being at least partially within the color filter element with said image area closely-adjacent the concave side of the element, the axis of the color filter element being positioned so that as the element rotates the filter segments traverse the image area in approximately the low-frequency direction.

2. In color television apparatus, in combination, an electronic scanning device comprising an envelope and an image area within said envelope and closely adjacent thereto, means for scanning said area in two dimensions in a plurality of side-by-side lines, and a rotatable substantially conical color filter element having a plurality of transparent color filter segments arranged therearound, the envelope of said scanning device being at least partially within the color filter element with said image area closely adjacent the concave side of the filter element, the axis of the color filter element extending laterally of the scanning area so that as the element rotates the filter segments traverse the image area in substantially the low-frequency direction.

3. In color television apparatus, in combination, a scanning device having a two-dimensional scanning area associated therewith, and a rotatable substantially conical color filter element having a plurality of transparent color filter segments arranged around the conical surface thereof, the vertex angle of said color filter ele-,

ment being acute and said scanning device being at least partially within the color filter element with the concave side of the element towardsaid scanning area as the element rotates.

4. In color television apparatus, in combination, an electronic scanning device comprising an envelope having a scanning area therewithin,

means for scanning said area in two'dimensions in a plurality of side-by-side lines, and a rotatable substantially conical color filter element having a plurality of transparent color filter segments arranged around the conical surface thereof, the vertex angle of said color filter element being acute and the envelope of said scanning device being at least partially within the color filter element and positioned so that as the element rotates the conical surface thereof passes adjacent the scanning device with the -lines on said luminescent surface, and a rotatable substantially conical color filter element having a plurality of transparentcolor filter segments arranged around the conical surface thereof, the vertex angle of said color filter element being acute and the bulbous portion of the receiver tube being at least partially within the color filter element with said luminescent image surface closely adjacent the concave surface of the element, the axis of the color filter element being positioned so that as the element rotates the filter segments traverse the image area in approximately the low-frequency direction.

6. In a color television receiver, in combination, a cathode ray receiver tube comprising an envelope having a bulbous portion and an elongated neck extending therefrom, a luminescent reproducing surface adjacent the bulbous portion of said envelope, means for reproducing twodimensional images on said luminescent surface in a plurality of side-by-side lines at field scanning frequency, a rotatable substantially conical color filter element having a plurality of transparent color filter segments arranged around the conical surface thereof, the vertex angle of said color filter element being acute and the bulbous portion of the receiver tube being at least partially within the color filter element with said luminescent image surface closely adjacent the concave surface of the element, the axis of the color filter element extending laterally of the scanning area so that as the element rotates the filter segments traverse the image area in substantially the low-frequency direction, means for rotating said color filter element at a speed such that filter segments traverse the image area at substantially field-scanning frequency, the ends of the filter segments towards the vertex being wider than the ends thereof toward the base of .the element and the segments being shaped so that as a segment traverses the image area. the lines of the image area are exhibited through the segment at substantially the instants the lines are scanned.

7. In a color television receiver, in combination, a cathode ray receiver tube comprising an envelope and a luminescent reproducing surface adjacent said envelope, means for reproducing two-dimensional images in a plurality of laterally extending side-by-side lines on said luminescent surface, and a rotatable substantially conical color filter element having a plurality of transparent color filter segments arranged around the conical surface thereof, the vertex angle of said color filter element being acute and said envelope being at least partially within the color filter element with said luminescent image surface closely adjacent the concave surface of the element, the axis of the color filter element extending laterally of the scanning area so that as the element rotates the filter segments traverse the image area in substantially the lowfrequency direction, and the front edge of the cone extending generally parallel to said luminescent reproducing surface in a lateral direction.

DAN P. DONCASTER. 

